Both gerunds and infinitives can be used as the subject or the complement of a sentence. However, as subjects or complements, gerunds usually sound more like normal, spoken English, whereas infinitives sound more abstract. In the following sentences, gerunds sound more natural and would be more common in everyday English. Infinitives emphasize the possibility or potential for something and sound more philosophical. If this sounds confusing, just remember that 90% of the time, you will use a gerund as the subject or complement of a sentence.

Examples:
1. Learning is important. normal subject
2. To learn is important. abstract subject - less common
3. The most important thing is learning. normal complement
4. The most important thing is to learn. abstract complement - less common